1Dx M2 Sensor Resolution - Back of envelop estimate
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filluppa said:
Question answered via my phrasing directly above. If you isolate the variable, noise varies with sensitivity. Note that by limiting the scope to ISO, the table from sensorgen doesn't apply, as it is based on pixel saturation, not equal input.
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filluppa said:
Dude, I exhaustively defined it.
But sure:
For a given input level (not "I went from iso100 to iso200 and in turn went from 1/100 to 1/200," rather, "I went from ISO100 to ISO200 and changed nothing else"), does noise vary with sensitivity?
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filluppa said:
Signal1 / Noise1
vs
Signal1 / Noise2
there are three possibilities. Noise1>Noise2, Noise1<Noise2, and Noise1=Noise2.
So, now that it is phrased explicitly about SNR where S is held constant and ISO varies, does SNR vary with ISO?
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filluppa said:
If increasing ISO with all else being equal results in a higher noise level, you can absolutely make the claim.
Your line of reasoning is similar to: I can halve my exposure time when I go from f/4 to f/2.8, so you can never claim that halving exposure time reduces light.
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You couldn't be this stupid. Leave everything alone. Go from ISO 100 to ISO 200. Same amount of signal. The ISO 200 photo is noisier. The signal isn't weaker, it's the same. Raising ISO doesn't weaken signal. Raising ISO in this case, introduces more noise. Understand?
Probably not.
Probably not.
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filluppa said:
I went to a Ted Nugent concert when I was a teen.
I remember the local news doing reports on concerts back then, 100 dB or more. Home owner were complaining miles away about rattling windows. Ted Nugent was one of the worse offenders.
Showing my age here, but Nugent debuted his song Free For All at the concert.
So wouldn't this be a comparison.
Ted Nugent playing Free For All in his living room with his band
VS
Ted Nugent playing Free For All amplified at the fair grounds.
Which would have more noise?
Of course the song has no more words or notes in the song.
But filluppa,
Explain this to us.
What happens to the noise and data when the signal is amplified by raising the ISO?
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L
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takesome1 said:
That's a good question. Let's look at what some individuals – three noteworthy and one banal – have said on that topic...
"The amplification process also means that any noise will be amplified too, and that is why we see more noise at higher ISOs." (Roger N. Clark)
"Increasing the Exposure Index...increases noise, degrading overall image quality." (Norman Koren, in the Imatest Documentation)
"Read noise increases with ISO, because any noise added from the sensor readout before ISO amplification is then amplified by the ISO gain amplifier." (Emil Martinec)
"At 400iso same exposure, ie the selected time, aperture, and ISO pictures are virtually identical. At about 800iso enters the noise of the Nikon images, this noise will affect the images adversely by the reproduction of detail suffers." (Mikael Risedal)
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filluppa said:
First, Eric Fossum's answer was in regard to the relationship between light levels and shot noise; not ISO setting and overall noise. Second, at no point in this thread have you made any consistent definition of noise. If you're so sure of yourself why don't you give us a clear definition of what you mean by noise. Third, in the table you keep posting, why do you think the read noise is decreasing? Do you think the electronics are generating less noise at lower light levels? Finally, does output referred noise, not noise-to-signal ratio but noise, increase with higher iso/gain settings?
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i can't believe this thread is still going (but nah, yes i can), but since it is i might as well throw in my 2 cents for internet fame...
since we are talking about an analog gain amplifier, not only does it amplify any noise present in the original signal, it also adds it's own thermal noise, crosstalk from other components, and distortion in the form of an imperfect response curve. an amplifier that did none of those things would be, like the perpetual motion machine, in defiance of the laws of physics.
since we are talking about an analog gain amplifier, not only does it amplify any noise present in the original signal, it also adds it's own thermal noise, crosstalk from other components, and distortion in the form of an imperfect response curve. an amplifier that did none of those things would be, like the perpetual motion machine, in defiance of the laws of physics.
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filluppa said:
You're referring to input referred noise, you clearly have zero understanding of what this means.
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filluppa said:
From an earlier post:
What's happening is that you can break the read noise down into two components: upstream of the amplifier and downstream of the amplifier (it should also be noted that some cameras use 2-stage amplifiers but the same approach is easily extensible to those as well). The resulting output referred noise becomes something like
No^2 = C^2*(N_us)^2 + (N_ds)^2
Where No is the output referred noise, N_us is the actual read noise of the upstream components, N_ds is the contribution of the downstream components, and C is the gain. To get the input referred noise, or how many electrons the read noise is equivalent to at the current gain setting, we simply use the relationship
Ni = (1/C)*No
where Ni is the input referred noise, which gives us
Ni^2 = (N_us)^2 + (1/C)^2*(N_ds)^2
Looking at both of these forms, you can see that as the gain becomes large, the relative contribution of the downstream noise becomes small; however, looking at the input referred noise should make it clear why you get an essentially constant read noise at high ISO in that table. The noise coming from the electronics doesn't change at all with ISO, but both their relative and absolute contributions to the final image absolutely changes.
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